Have you tried the stop-start method? I watched a Ted Talk from a sex educator who said it's an effective technique for preventing premature ejaculation. Something you would practice for a while.

Ever thought about consulting with a sex therapist? I had a friend who said it really helped her. I don't know what the specific issue was but something sexual that was not going well with her bf. Anyway, she said the therapist was amazing and really helped them to get back on track sexually.

Your problem does not sound medical at all. Though I'm not a doc

Hope this helps a bit. I wish you well